1. Field of the Invention
The present invention-relates to an objective actuator which is set for example, with an optical pick-up device.
2. Related Art
The optical pick-up device is used for writing data signals into and reading the same out of an optical disk as a recording media in an optical disk device.
In the optical pick-up device, it is essential to exactly focus laser beams at data pits on the optical disk. To this end, an objective actuator is used which drives the objective or object lens to look constantly in the direction of the optical axis irrespective of vibration and swing motions of the optical disk.
An example of the conventional objective actuators used for the optical pick-up device, for example, will be described. An objective holder is supported by a support shaft in such a manner so that it is rotatable about the support shaft and movable in the axial direction of the support shaft. A focusing drive coil and a tracking drive coil are mounted on the objective holder. A focusing drive magnet and a tracking drive magnet are mounted on a yoke. The arrangement is made such that the focusing and tracking drive coils face the focusing and tracking drive yokes, respectively. This objective actuator is disclosed in Published Unexamined Japanese Patent Application No. Hei. 1- 307029, filed by the applicant of the present patent application.
A key portion of the conventional objective actuator is illustrated in FIG. 22. A first yoke 91 and a second yoke 93, both being pressed shaped, are disposed as shown and laminated one upon the other by adhesive, for example. A support shaft 90 is fixed by press fitting it into the center hole 98 of the first yoke 91. An objective holder 97 is supported by the support shaft 90 in a manner that it is rotatable about the support shaft 90 and movable in the axial direction of the support shaft 90. An object lens, not shown, and a drive coil 96 are secured to the objective holder 97. The drive coil 96 confronts with the inner circumferential surface of a drive magnet 95, which is secured to the inner circumferential surface of the first yoke 91 in a state that a proper gap is present between the drive coil 96 and the inner circumferential surface of a drive magnet 95. The drive coil 96 consists of a focusing drive coil and a tracking drive coil. The drive magnet 95 consists of a focusing drive magnet and a tracking drive magnet. For focusing control, a controlled current is fed to the focusing drive coil, so that the object lens, together with the objective holder 97, is moved in the axial direction of the support shaft 90. For tracking control, a control current is fed to the tracking drive coil, so that the object lens, together with the objective holder 97, is turned about the support shaft 90.
In the conventional objective actuator, the support shaft 90 is fixed by press fitting it into the center hole 98 of the first yoke 91, as described above. Accordingly, the verticality of the center hole 98 of the first yoke 91 is slightly lost when the first yoke 91 is press shaped. The support shaft 90 is also slightly lost in its verticality when it is press fit into the center hole 98. Those slight deviations of verticality are accumulated to create a noticeable inclination of the support shaft 90. The inclination of the support shaft 90 adversely affects the performances of the assembled product or the objective actuator.
Further, it brings about complication of the assembling work, and hence elongation of the time to assemble. To secure a smooth shift of the objective holder 97 along the support shaft 90 and a smooth turn of the objective holder 97 about the support shaft 90, the outer surface of the support shaft 90 is coated with resin (e.g., Teflon, trade name). In this case, the support shaft 90 must be coated except the insertion part 94 of the support shaft where it is inserted into the center hole 98 of the first yoke 91 for fixing the support shaft 90. For this reason, before the coating is performed, the insertion part 94 is masked so as to allow only the portion of the support shaft 90 along which the objective holder 97 moves to be coated. As a result, the coating process is made complicated. When the support shaft 90 is press fit into the center hole of the first yoke 91, the coating surface of the support shaft tends to be damaged.